A few months ago, the dog presented with a nonspecific lameness, severe progression for two weeks.
Physical exam: ambulatory paraparesis with ataxia of the hind limbs, painful palpation at the thoracolumbar area.
Diagnostics: MR exam with 0.3 T magnet. Patient anesthetized and scanned in lateral recumbency, position head first. Multiple sequences of the mid thoracic to mid lumbar spine, including T2, T1 dor MPR pre and post contrast, STIR and BASG sequences.
The MR myelogram shows spinal compression at T12-13. There is a space occupying lesion from the left of the 12th thoracic vertebra including the head of the left 12th rib that is invading the spinal canal with severe spinal cord compression. There is a thin uniform T2 and STIR hyperintense rim on the mass. The rim had moderate uniform contrast enhancement. The small remnant of the spinal cord in the ventral right spinal canal has a smaller diameter compared to the adjacent spinal cord. No other lesions were detected.
MR diagnosis: Cartilaginous exostosis T12 with spinal cord compression.
Differential Diagnosis: Vertebral malformation, Trauma
The fluid- isointense cap on a skeletal lesion in a young dog is very typical for a cartilage- covered exostosis and differential diagnosis were therefore unlikely. The unusual disease is mainly seen in young animals since the exostosis develops via enchondral ossification in the growing bone. Therefore only bones which develop via enchondral ossification are affected and predilection sites are vertebrae, ribs, long bones, scapula and pelvis. If the disease occurs at several sites, it is called multiple cartilaginous exostosis. In the dog presented here, a whole body CT examination was performed to screen for other lesions and for surgical planning, but other sites were not detected. The clinical signs depend on the location and in this case the spinal cord compression led to nonspecific neurological dysfunction. The dog underwent surgery with excision of the exostosis. After several days there was mild improvement of the clinical symptoms and the dog went home. There are two main theories about the etiology of the disease: a dyschondroplasia in the periphery of the growth plates,or a disturbance of the periosteum due to physical stress. A malignant transformation into osteosarcoma is possible and the thickness of the cartilage cap visible as a fluid isointense rim on the lesion might indicate probability of malignant transformation.
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